CMS-PAS-BPH-14-009

CMS-PAS-BPH-14-009
Dependence of the $\Upsilon$ (nS) production ratios on charged particle multiplicity in pp collisions at $\sqrt{s}=$ 7 TeV
CMS Collaboration
October 2016

Abstract: The ratios of the cross section of the $\Upsilon$ (nS) mesons with $\|y\|<1.2$ are studied as a function of the number of charged particles with $p_{\mathrm{T}}>$ 0.4 GeV and $\|\eta\|<$ 2.4 produced in pp collisions at $\sqrt{s}=$ 7 TeV. Evidence of a decrease of the ratios between the higher and the lower mass states is observed, that is more pronounced at lower $p_{\mathrm{T}}$ . For $\Upsilon$ (nS) mesons of transverse momentum greater than 7 GeV, this effect is studied as a function of the underlying event sphericity, and of the distribution of charged particles with respect to the $\Upsilon$ (nS) direction.
Links: CDS record (PDF) ; CADI line (restricted) ; These preliminary results are superseded in this paper, JHEP 11 (2020) 001. The superseded preliminary plots can be found here.

Figures	Summary	References	CMS Publications

Figures
png pdf	Figure 1: Fit to the mass spectrum of dimuon candidates with $p_{\mathrm{T}} >$ 7 GeV and $\|y\| <$ 1.2, in two ranges of charged particle multiplicity 0-10 (a) and 100-140 (b).
png pdf	Figure 1-a: Fit to the mass spectrum of dimuon candidates with $p_{\mathrm{T}} >$ 7 GeV and $\|y\| <$ 1.2, in two ranges of charged particle multiplicity 0-10.
png pdf	Figure 1-b: Fit to the mass spectrum of dimuon candidates with $p_{\mathrm{T}} >$ 7 GeV and $\|y\| <$ 1.2, in two ranges of charged particle multiplicity 100-140.
png pdf	Figure 2: Production ratios for $\Upsilon$ (2S)/ $\Upsilon$ (1S) and $\Upsilon$ (2S)/ $\Upsilon$ (1S) in (a), and $\Upsilon$ (3S)/ $\Upsilon$ (2S) in (b) as a function of N $^{\|\eta \|<2.4}_{tracks}$ . The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 2-a: Production ratios for $\Upsilon$ (2S)/ $\Upsilon$ (1S) and $\Upsilon$ (2S)/ $\Upsilon$ (1S) as a function of N $^{\|\eta \|<2.4}_{tracks}$ . The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 2-b: Production ratios for $\Upsilon$ (3S)/ $\Upsilon$ (2S) as a function of N $^{\|\eta \|<2.4}_{tracks}$ . The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 3: Mean $p_{\mathrm{T}}$ for the three $\Upsilon$ states, as well as of the sideband background , as a function of multiplicity. The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares are the systematic uncertainties.
png pdf	Figure 4: Production ratios vs multiplicity for $\Upsilon$ (2S)/ $\Upsilon$ (1S) in (a), $\Upsilon$ (3S)/ $\Upsilon$ (1S) in (b), $\Upsilon$ (3S)/ $\Upsilon$ (2S) in (c) in different regions of ${p_{\mathrm {T}}}$ . $\Upsilon$ states satisfy $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 4-a: Production ratios vs multiplicity for $\Upsilon$ (2S)/ $\Upsilon$ (1S) in different regions of ${p_{\mathrm {T}}}$ . $\Upsilon$ states satisfy $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 4-b: Production ratios vs multiplicity for $\Upsilon$ (3S)/ $\Upsilon$ (1S) in different regions of ${p_{\mathrm {T}}}$ . $\Upsilon$ states satisfy $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 4-c: Production ratios vs multiplicity for $\Upsilon$ (3S)/ $\Upsilon$ (2S) in different regions of ${p_{\mathrm {T}}}$ . $\Upsilon$ states satisfy $\|y\|<$ 1.2, while tracks are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic ones.
png pdf	Figure 5: In (a), the schematic view of the tracks kinematic regions in the azimuthal plane with respect to the $\Upsilon$ (nS) direction. In (b), the production ratios for $\Upsilon$ (2S) and $\Upsilon$ (3S) over $\Upsilon$ (1S) as a function of N $^{\|\eta \|<2.4}_{tracks}$ measured in the kinematic regions shown in (a). The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta ^{tracks}\| <$ 2.4 and ${p_{\mathrm {T}}} ^{tracks} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic one.
png pdf	Figure 5-a: The schematic view of the tracks kinematic regions in the azimuthal plane with respect to the $\Upsilon$ (nS) direction.
png pdf	Figure 5-b: The production ratios for $\Upsilon$ (2S) and $\Upsilon$ (3S) over $\Upsilon$ (1S) as a function of N $^{\|\eta \|<2.4}_{tracks}$ measured in the kinematic regions shown in Fig. 5-a. The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta ^{tracks}\| <$ 2.4 and ${p_{\mathrm {T}}} ^{tracks} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares show the systematic one.
png pdf	Figure 6: Production ratios as a function of N $^{\|\eta \|< 2.4}_{tracks}$ for $\Upsilon$ (2S)/ $\Upsilon$ (1S) and $\Upsilon$ (3S)/ $\Upsilon$ (1S), in different intervals of events sphericity. The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares are the systematic ones.
png pdf	Figure 6-a: Production ratios as a function of N $^{\|\eta \|< 2.4}_{tracks}$ for $\Upsilon$ (2S)/ $\Upsilon$ (1S) and $\Upsilon$ (3S)/ $\Upsilon$ (1S), in three categories based on the number of charged particles produced in a cone $\Delta \mathrm{R} <$ 0.5 around the $\Upsilon$ direction. The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares are the systematic ones.
png pdf	Figure 6-b: Production ratios as a function of N $^{\|\eta \|< 2.4}_{tracks}$ for $\Upsilon$ (2S)/ $\Upsilon$ (1S) and $\Upsilon$ (3S)/ $\Upsilon$ (1S), in different intervals of events sphericity. The $\Upsilon$ states satisfy ${p_{\mathrm {T}}} >$ 7 GeV and $\|y\|<$ 1.2, while charged particles are counted for $\|\eta \| <$ 2.4 and ${p_{\mathrm {T}}} >$ 0.4 GeV. Error bars represent statistical uncertainties, while empty squares are the systematic ones.

Summary

We have measured the ratio between the

$\Upsilon$ (nS) yields in pp collisions at

$\sqrt{s}=$ 7 TeV as a function of the number of charged particles produced with

$|\eta| <$ 2.4 and

$p_{\mathrm{T}} >$ 0.4 GeV. We observe a significant reduction of the ratios of high over low mass

$\Upsilon$ yields with increasing multiplicity. This result extends the observation in pp and pPb collisions in Ref. [1]. The effect is visible in different ranges of

$p_{\mathrm{T}}$ , but decreases with increasing

$p_{\mathrm{T}}$ . With the larger statistic available for

$\Upsilon$ (nS) with

$p_{\mathrm{T}} >$ 7 GeV, different observables were studied in order to obtain a better description of the phenomenology in connection with the underlying event. We found no link between the relative direction of the charged particles with respect to the direction of the

$\Upsilon$ and no strong dependence on the event sphericity, while we observe a flattening of the

$\Upsilon$ (2S) /

$\Upsilon$ (1S) multiplicity dependence when a large number of particles is present in a strict cone around the

$\Upsilon$ direction.

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